CN114928391A - Waveform design and demodulation method suitable for high-speed frequency hopping - Google Patents
Waveform design and demodulation method suitable for high-speed frequency hopping Download PDFInfo
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- H—ELECTRICITY
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
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- H04B7/15564—Relay station antennae loop interference reduction
- H04B7/15585—Relay station antennae loop interference reduction by interference cancellation
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- H—ELECTRICITY
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- H—ELECTRICITY
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
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Abstract
The invention discloses a waveform design and demodulation method suitable for high-speed frequency hopping, and relates to a transmission technology capable of effectively improving the anti-interference capability of a system in the field of satellite communication. The invention realizes high-speed frequency hopping signal synchronization by various technologies such as specific frame structure design, synchronous sequence capture and tracking, high-speed frequency comprehensive control, diversity reception and the like, realizes the functions of interference avoidance, interference elimination and the like by means of interference detection, interference processing and the like, and realizes the strong anti-interference function of a communication system. It also has the survivability and robustness of a frequency hopping system. The method is particularly suitable for improving the anti-interference capability of the satellite communication system.
Description
Technical Field
The invention relates to a waveform design and demodulation method suitable for high-speed frequency hopping in the field of satellite communication, in particular to a method suitable for improving the anti-interference capability of a high-speed frequency hopping system in satellite communication.
Background
In modern communication and countermeasure environments centered on information networks, communication interference resistance is an important guarantee for reliable information transmission. Modern jamming reconnaissance devices present unprecedented challenges to current jamming-resistant communications.
The united states is at an international leading level in satellite communications defense: the MILSTAR satellite communication system and the advanced ultra high frequency satellite communication system (AEHF) provide effective guarantee for the transmission of important information in the United states. The domestic existing communication equipment mostly adopts a single frequency band, and has high speed, high frequency band, low speed, low frequency band and a plurality of categories in the aspect of data speed; the interference resistance systems of different devices are different, which brings difficulty of cooperative communication. The communication equipment is difficult to adapt to complex interference environment, the anti-interference capability is limited, the anti-interference means is single, and the continuously developed interference and reconnaissance technology is difficult to resist.
Disclosure of Invention
The invention provides a high-speed frequency hopping waveform design and demodulation method for overcoming the defects of the existing frequency hopping transmission waveform and improving the anti-interference capability, and provides a special transmission waveform which can normally work under the condition that the frequency hopping rate is as high as 18000 hops/second. The invention realizes high-speed frequency hopping signal synchronization by various technologies such as specific frame structure design, synchronous sequence capture and tracking, high-speed frequency comprehensive control, diversity reception and the like, realizes the functions of interference avoidance, interference elimination and the like by means of interference detection, interference processing and the like, and realizes the strong anti-interference function of a communication system. It also has the survivability and robustness of a frequency hopping system. The method is particularly suitable for improving the anti-interference capability of the satellite communication system.
The technical scheme adopted by the invention is as follows:
a waveform design and demodulation method suitable for high-speed frequency hopping comprises the following steps:
(1) designing a frame structure, wherein each frame comprises a plurality of subframes, and each subframe comprises a synchronization sequence, control information, TOD information and service information; the synchronization sequence changes according to the time information period, N subframes are a period, and N is an integer greater than 1;
(2) the satellite transponder transmits a synchronization sequence and TOD information according to a frame structure;
(3) the ground station terminal roughly estimates TOD through initial time information, forms a frequency set according to the TOD information, receives signals on all frequency points and captures a synchronization sequence;
(4) after the acquisition is successful, timing estimation is carried out through a synchronization sequence to recover a synchronous clock as a ground station terminal demodulation clock;
(5) the ground station terminal recovers TOD information from the received signal by adopting differential demodulation and decoding, generates a frequency hopping pattern, generates frequency hopping frequency points through frequency synthesis and realizes frequency hopping synchronization;
(6) after frequency hopping synchronization, the ground station terminal sends and receives data according to a frequency hopping frame plan to carry out normal communication;
(7) after frequency hopping synchronization, the satellite transponder performs interference detection on the signal of each time slot in a power detection mode, and frequency points where the signals with abnormal power values are located are removed from the frequency set, so that interfered frequencies are automatically avoided;
(8) the ground station terminal accumulates the received service signal for multiple times in a diversity reception mode.
Wherein, in the step (1): the length L of the synchronization sequence is determined according to the symbol rate of frequency hopping transmission by adopting a pseudo-random sequence-m sequence as the synchronization sequence; wherein the synchronization sequence varies over time.
Wherein the step (7) specifically comprises the following steps:
(701) performing matched filtering on the signal sampling points to filter out-of-band noise and interference;
(702) carrying out power statistics on each time slot signal, and carrying out statistics on the average power of the signal in one time slot;
(703) performing power accumulation and average on the signals in a set time period to obtain a power reference threshold P th ；
(704) The signal power of each time slot is compared with a power reference threshold P th Comparing and judging whether the signal power is larger than a power reference threshold P th If the signal is not larger than the preset value, the signal is considered to be normal;
(705) and eliminating the frequency point where the power value abnormal signal is positioned from the frequency set, and avoiding the interfered frequency.
Compared with the background technology, the invention has the following advantages:
1. the design of the invention is very suitable for capturing and tracking the carrier frequency of the high-speed frequency hopping transmission signal, and the frame structure design is very suitable for realizing FPGA.
2. The invention can carry out multi-rate hybrid demodulation and has the characteristics of variable data rate, intermediate frequency, modulation mode and the like.
3. The diversity reception and interference detection technology adopted by the invention can effectively improve the anti-interference capability of the system.
Drawings
Fig. 1 is a schematic diagram of the frequency hopping frame structure of the present invention.
Fig. 2 is a schematic diagram of the frequency hopping synchronization and demodulation process of the present invention.
Fig. 3 is a schematic diagram of automatic interference avoidance according to the present invention.
Detailed Description
Referring to fig. 1 to 3, a frequency hopping frame structure of a satellite communication system is shown in fig. 1, and a satellite communication system repeater transmits information according to the frequency hopping frame structure; as shown in fig. 2, after the terminal of the ground station in the satellite communication system is powered on, the acquisition and synchronization of the hopping pattern are completed first, and then the demodulation of the service signal is performed. The automatic interference avoidance function is shown in fig. 3, the repeater of the satellite communication system can update the frequency hopping frequency set according to the channel interference detection result to avoid interference, and the ground station terminal can adopt diversity processing according to the interference detection result to improve the anti-interference capability.
The present invention will be further described below.
The invention comprises the following steps:
(1) in order to facilitate the transmission of frequency hopping signals, a special frame structure is designed first. Each frame comprises N subframes, and each subframe comprises a synchronization sequence, control information, time information (TOD) and service information; the synchronization sequence changes according to the time information period, and N subframes are one period;
the synchronization sequence is used for frequency hopping synchronization acquisition, determining the starting position of each hop signal and assisting in high dynamic carrier frequency acquisition tracking. After the acquisition is finished, the synchronization sequence is used for clock tracking; the control information is used for network access and service application; time information (TOD) is used to indicate a frequency hopping pattern; the service information is used to transmit voice, image, etc.
(2) The satellite transponder sends a synchronization sequence and TOD information according to a frame structure, and after the satellite transponder is started, broadcasting, synchronization and service information are issued according to a frame format.
(3) The ground station terminal roughly estimates TOD through initial time information, forms a frequency set according to the TOD information, receives signals on the frequency points and captures a synchronous sequence;
and the ground station terminal receives the signal sent by the satellite transponder, captures the synchronization sequence in a frequency point watching mode and realizes the coarse synchronization of the frequency hopping frequency points.
(4) And after the acquisition is successful, timing estimation is carried out through the synchronous sequence to recover a synchronous clock as a ground station terminal demodulation clock.
(5) And the signals received by the ground station terminal adopt differential demodulation and decoding to recover TOD accurate information for generating frequency hopping patterns, and the frequency hopping patterns are sent to the frequency synthesizer to generate frequency hopping frequency points, so that the frequency points are completely synchronous with the satellite transponder, and frequency hopping synchronization is completed.
(6) After the frequency hopping synchronization, the service station of the satellite communication system enters a normal communication process. And the ground station terminal sends and receives data according to the frequency hopping frame plan to complete the communication function.
(7) After frequency hopping synchronization, the satellite transponder performs interference detection on the signal of each time slot in a power detection mode, and frequency points where the signals with abnormal power values are located are removed from the frequency set, so that the interfered frequency is automatically avoided; the specific method comprises the following steps:
firstly, carrying out matched filtering on signal sampling points to filter out-of-band noise and interference;
carrying out power statistics on each time slot signal, and carrying out statistics on the average power of the signal in one time slot;
and thirdly, performing power accumulation and averaging in a sliding manner. For signals in a period of time, generally N (N is an integer greater than 1) time slots are taken, power accumulation and averaging are performed to obtain a power reference threshold P th 。
And fourthly, power comparison. For the signal of each time slot, the interference detection is carried out by power comparison, namely the signal power of each time slot is compared with P th Comparing, judging whether the power is larger than the power reference threshold P th If it is greater than P th The power is considered abnormal, if not more than P th If the signal is normal, the signal is considered normal;
outputting abnormal indication. The frequency point where the power value abnormal signal is located is removed from the frequency set, the interfered frequency is avoided, and the automatic interference avoiding function is realized;
(8) the ground station terminal accumulates the received service signal for multiple times in a diversity reception mode.
And completing the waveform design and demodulation suitable for high-speed frequency hopping.
Claims (3)
1. A waveform design and demodulation method suitable for high-speed frequency hopping is characterized by comprising the following steps:
(1) designing a frame structure, wherein each frame comprises a plurality of subframes, and each subframe comprises a synchronization sequence, control information, TOD information and service information; the synchronization sequence changes according to a time information period, N subframes are a period, and N is an integer greater than 1;
(2) the satellite transponder transmits a synchronization sequence and TOD information according to a frame structure;
(3) the ground station terminal roughly estimates TOD through initial time information, forms a frequency set according to the TOD information, receives signals on all frequency points and captures a synchronization sequence;
(4) after the acquisition is successful, timing estimation is carried out through a synchronization sequence to recover a synchronous clock as a ground station terminal demodulation clock;
(5) the ground station terminal recovers TOD information from the received signal by adopting differential demodulation and decoding, generates a frequency hopping pattern, generates frequency hopping frequency points through frequency synthesis and realizes frequency hopping synchronization;
(6) after the frequency hopping synchronization, the ground station terminal sends and receives data according to a frequency hopping frame plan, and normal communication is carried out;
(7) after frequency hopping synchronization, the satellite transponder performs interference detection on the signal of each time slot in a power detection mode, and frequency points where the signals with abnormal power values are located are removed from the frequency set, so that interfered frequencies are automatically avoided;
(8) the ground station terminal accumulates the received service signal for multiple times in a diversity reception mode;
and completing the waveform design and demodulation suitable for high-speed frequency hopping.
2. The method for waveform design and demodulation suitable for high speed frequency hopping according to claim 1, wherein in the step (1): the length L of the synchronization sequence is determined according to the symbol rate of frequency hopping transmission by adopting a pseudo-random sequence-m sequence as the synchronization sequence; wherein the synchronization sequence varies over time.
3. The method according to claim 1, wherein the step (7) comprises the following steps:
(701) performing matched filtering on the signal sampling points to filter out-of-band noise and interference;
(702) carrying out power statistics on each time slot signal, and carrying out statistics on the average power of the signal in one time slot;
(703) accumulating and averaging the power of the signals in a set time period to obtain a power reference threshold P th ；
(704) The signal power of each time slot is compared with a power reference threshold P th Comparing and judging whether the signal power is larger than a power reference threshold P th If the signal is not larger than the preset value, the signal is considered to be normal;
(705) and eliminating the frequency point where the power value abnormal signal is positioned from the frequency set, and avoiding the interfered frequency.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117040610A (en) * | 2023-08-23 | 2023-11-10 | 北京慧清科技有限公司 | ACM frequency-selecting waveform method suitable for FDD scattering communication system |
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2022
- 2022-06-10 CN CN202210649908.XA patent/CN114928391A/en active Pending
Non-Patent Citations (3)
| Title |
|---|
| 李一阳: "基于TOD法的跳频同步研究与实现", 《CNKI优秀硕士学位论文全文库》, 15 April 2018 (2018-04-15), pages 1 - 3 * |
| 王丁: "跳频通信系统中同步技术的研究与仿真分析", 《CNKI优秀硕士学位论文全文库》, 15 September 2014 (2014-09-15), pages 2 - 3 * |
| 王赛宇: "跳频传输帧结构设计与频率估计研究", 《信号与信息处理》, 22 August 2014 (2014-08-22), pages 26 * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117040610A (en) * | 2023-08-23 | 2023-11-10 | 北京慧清科技有限公司 | ACM frequency-selecting waveform method suitable for FDD scattering communication system |
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